3/1/20

1

L09: Bacterial Genetics

BIOL 153/LBlack Hills State Univ.Ramseys

I. Nucleic acids

A. Significance

• Compose DNA and RNA

• Genetic code for proteins

• Energy carriers (ATP, NADPH)

B. Structure

Fig. 2-18Raven p. 29

II. DNAA. Nucleotides

adenine, thymine cytosine, guanine

Fig. 2-20Raven p. 30

3/1/20

2

II. DNAB. The double helix

Fig. 9-1Raven p. 175

1. Pairing of nitrogenous bases (of nucleotides)

1. Pairing of nitrogenous bases (of nucleotides)

Adenine (A) Thymine (T)

Cytosine (C) Guanine (G)

1. Pairing of nitrogenous bases (of nucleotides)

Adenine (A) Thymine (T)

Cytosine (C) Guanine (G)

2. Twisting ladder

Frame of ladder (strong bonds):

sugars + phosphate groups

Rung of ladder (weak bonds):

nitrogenous bases

3. Antiparallel strands

connected DNA strands run in opposite directions

3/1/20

3

strong bonds

weak bonds Not parallel!!!

C. Instructions for making protein 1. DNA sequences

ATGGTCTTACAC...........

3/1/20

4

1. DNA sequences

ATGGTCTTACAC...........

2. Codons

ATG GTC TTA CAC ......Methionine – Valine – Leucine – Histidine .......

D. Noncoding DNA

DNA that does not encode a protein

noncoding DNA may (not) have a genetic function!

E. Central Dogma of Molecular Biology

• Gene => segment of DNA

• 1 gene => 1 protein

DNA à RNA à Protein

DNA à RNA à Protein

Transcription Translation

Central Dogma: Transcription & Translation

Fig. 9-8Raven p. 180

3/1/20

5

III. Prokaryotic genetics A. Chromosome

• Circular

• In cytoplasm

• Essential genes

B. Plasmid

• Extra-chromosomal

• Non-essential genes

• Medically important

C. Asexual reproduction

• Makes genetically identical cells

• Mutations sometimes occur

3/1/20

6

C. Asexual reproduction

• Makes genetically identical cells

• Mutations sometimes occur

• Three major mechanisms

1. Fission

Fig. 13-8Raven p. 261

• Genetic material duplicates, then cell divides

1. Fission

Fig. 13-8Raven p. 261

• Genetic material duplicates, then cell divides

1. Fission

Fig. 13-8Raven p. 261

• Genetic material duplicates, then cell divides

1. Fission

Fig. 13-8Raven p. 261

Mother cell

Daughter cells

• Genetic material duplicates, then cell divides

2. Budding

• Cell divides afterunequal growth

• Bud may have different function

3/1/20

7

2. Budding

• Cell divides afterunequal growth

• Bud may have different function

Bud

Strand

ParentCell

2. Budding

• Cell divides afterunequal growth

• Bud may have different function Mother cell

Daughter cell Bud

Strand

ParentCell

Caulobactor crescentus

Hyphomicrobium sp. Mycoplasma pneumoniae

Examples of budding bacteria

Freshwater Soil Disease

3. Fragmentation

• Aggregations split into fragments

• Bud breaks free

D. Genetic variation with asexual reprod.

• In theory... genetically identical

• In reality... mutations happen

because prokaryotes reproduce quickly, rare mutations sometimes spread!

E. Gene transfer

• Bacteria promiscuous, genetically simple

• Receive + incorporate DNA from other bacteria

• Three mechanisms

3/1/20

8

1. Transformation

pick up DNA from environment

2. Conjugation

receive DNA from another bacterium

Pilus

Fig. 13-4Raven p. 259

pilus

3. Transduction

virus carries DNA from donor to recipient

F. Antibiotic resistance

bacteria not killed by previously potent antibiotics

• Natural resistance (pre-antibiotic)

• Mutation

• Horizontal gene transfer

F. Antibiotic resistance

3/1/20

9

• Natural resistance (pre-antibiotic)

• Mutation

• Horizontal gene transfer

F. Antibiotic resistance Horizontal gene transfer• Same or different species

• Conjugation is primary mechanism

• Can be multiple resistances

Resistance plasmid Medical use of phage• Targets specific bacteria

• Low chance of resistance

3/1/20

10

Medical use of phage• Targets specific bacteria

• Low chance of resistance

• Hard to regulate

• Expensive to develop, little profit